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\section{\usemenu{slac-pub-7056::context::slac-pub-7056-0-0-10}{ Future Directions }}\label{section::slac-pub-7056-0-0-10}
The light-cone formalism is a very promising framework for the study
of hadronic structure. The fact that it allows a precise definition
of the parton model means that the light-cone wavefunctions are the
most natural way of encoding hadronic structure. The ability to
boost states easily---manifested in the frame-independence of the
formalism---is another major advantage. Finally, light-cone
quantization offers the best hope for deriving a constituent {\em
approximation} to hadronic structure from QCD. In any other frame,
the need to understand the constituents as quasi-particles makes
building a connection to a CQM essentially hopeless.
As we have emphasized in these lectures, the proton is represented
in QCD at a given light-cone time $x^+ = t+z$ as a superposition of
quark and gluon Fock states $\vert uud\rangle,\vert uudg\rangle,
\vert uud Q \overline Q\rangle$, etc. Thus when the proton is
expanded on a free quark and gluon basis, it is a fluctuating system
of arbitrarily large particle number. The light-cone wavefunctions
$\psi_n(x_i, k_{\perp i}, \lambda_i)$ are the probability amplitudes
which describe the projections of the proton state on this Hilbert
space. The structure functions measured in deep inelastic lepton
scattering are directly related to the light-cone $x$ momentum
distributions of the quarks and gluons determined by the
$\vert\psi_n\vert^2$. Another interesting measure of the proton's
structure involves examining the system of hadrons produced in the
proton's fragmentation region when one quark is removed, i.e., the
proton's ``fracture functions'' \cite{113}. At HERA, the particles
derived from the spectator $\bar 3_C$ system which are intrinsic to
the proton's structure are produced in the proton beam direction
with approximately the same rapidity as that of the proton at
relatively small transverse momentum \cite{84}. Thus in
high-energy $e p$ collisions, the electron resolves the
diffractively-excited proton, revealing the correlations of the
spectator quarks and gluons in its light-cone Fock components with
invariant mass extending up to the energy of the collision.
It is of particular interest to examine the fragmentation of the
proton when the electron strikes a light quark and the interacting
Fock component is the $\vert uud c \bar c \rangle$ or $\vert uud b
\bar b \rangle$ state. These Fock components correspond to
intrinsic charm or intrinsic bottom quarks in the proton
wavefunction. Since the heavy quarks in the proton bound state have
roughly the same rapidity as the proton itself, the intrinsic heavy
quarks will appear at large $x_F$. One expects heavy quarkonium and
also heavy hadrons to be formed from the coalescence of the heavy
quark with the valence $u$ and $d$ quarks, since they have nearly
the same rapidity. Since the heavy and valence quark momenta
combine, these states are preferentially produced with large
longitudinal momentum fractions.
A recent analysis by Harris, Smith and Vogt \cite{114} of the
excessively large charm structure function of the proton at large
$x$ as measured by the EMC collaboration at CERN yields an estimate
that the probability $P_{c \bar c}$ that the proton contains
intrinsic charm Fock states is of the order of 0.6\%. In the case
of intrinsic bottom, PQCD scaling predicts
\begin{equation}
P_{ b \bar b}=P_{c \bar c} {m^2_\psi\over m^2_\Upsilon}
{\alpha^4_s(m_b) \over \alpha^4_s(m_c)}\; ,
\end{equation}
more than an order of magnitude smaller. If super-partners of the
quarks or gluons exist they must also appear in higher Fock states
of the proton, such as $\vert uud ~{\rm gluino}~ {\rm
gluino}\rangle$. At sufficiently high energies, the diffractive
excitation of the proton will produce these intrinsic quarks and
gluinos in the proton fragmentation region. Such supersymmetric
particles can bind with the valence quarks to produce highly unusual
color-singlet hybrid supersymmetric states such as $\vert uud ~{\rm
gluino}\rangle$ at high $x_F.$ The probability that the proton
contains intrinsic gluinos or squarks scales with the appropriate
color factor and inversely with the heavy particle mass squared
relative to the intrinsic charm and bottom probabilities. This
probability is directly reflected in the production rate when the
hadron is probed at a hard scale $Q$ which is large compared to the
virtual mass ${\cal M}$ of the Fock state. At low virtualities, the
rate is suppressed by an extra factor of $Q^2/{\cal M}^2.$ The
forward proton fragmentation regime is a challenge to instrument at
HERA, but it may be feasible to tag special channels involving
neutral hadrons or muons. In the case of the gas jet fixed-target
$ep$ collisions at ELFE or HERMES, the target fragments emerge at
low velocity and large backward angles, and thus may be accessible
to precise measurement.
As we have outlined in these lectures, the light-cone Fock
representation of quantum chromodynamics provides both a tool and a
language for representing hadrons as fluctuating composites of
fundamental quark and gluon degrees of freedom. Light-cone
quantization provides an attractive method to compute this structure
from first principles in QCD. However, much more progress in theory
and in experiment will be needed to fulfill this promise.
\vspace{.5in}
\centerline{\bf Acknowledgements}
\noindent
It is a pleasure to thank the organizers of the ELFE Workshop and
Summer School, in particular S. D. Bass, for their efforts and
hospitality. S.J.B. also wishes to thank J. Hiller, P. Hoyer, O.
Jacob, G. P. Lepage, H. J. Lu, A. Mueller, H.-C. Pauli, S. Pinsky,
W.-K. Tang, F. Schlumpf, and R. Vogt for helpful conversations.
D.G.R. is grateful to M. Burkardt, K. Hornbostel and R. J. Perry for
many valuable discussions and comments on portions of the
manuscript. The work of S.J.B. was supported by the Department of
Energy, contract No. DE-AC03-76SF00515. D.G.R was supported by the
National Science Foundation under Grants Nos. PHY-9203145,
PHY-9258270, and PHY-9207889.
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